Sens. Bernie Sanders (I-Vt.), Elizabeth Warren (D-Mass.) and Jeff Merkley (D-Ore.) called on General Dynamics, the third largest federal contractor, to respond to formal complaints that the company is participating in systemic wage theft and coercive anti-union practices at its federally contracted call centers.

“Our respective offices recently met with GDIT employees from multiple CMS call centers and were deeply disturbed to hear reports of wage theft and unfair labor practices at these worksites. We were especially startled that these may not be isolated instances but may in fact reflect systemic and repeated labor violations by GDIT,” the senators wrote. “Given the severity of the allegations at hand, we request that GDIT comment in a timely fashion, on what actions it is taking to ensure compliance with wage and hour laws while our offices contemplate a response to the Department of Labor and any other agencies who work on behalf of American workers.”

A recent New York Times story details a complaint filed by the Communications Workers of America on behalf of General Dynamics Information Technology employees that alleges workers are owed more than $100 million in back wages as a result of being misclassified in lower-paying job designations. This complaint is not the first one to be filed against the company. According to Department of Labor records, General Dynamics has agreed to pay nearly $4 million in back wages at its call centers for violations since 2007.

In February, the National Labor Relations Board issued a complaint against General Dynamics for allegedly violating labor laws at a call center in Alexandria, Virginia, by threatening employees and falsely telling workers that it would take an “act of Congress” to raise their wages.

The senators’ request comes after their offices met with workers employed by General Dynamics Information Technology, a business unit of the company, which operates call centers that respond to Medicare inquiries as part of a 10-year contract with the Centers for Medicare and Medicaid Services.